A recording method using an inkjet printer, which is a representative method among various color recording methods, is for performing recording by generating small ink droplets and attaching the ink droplets to a variety of record-receiving materials (paper, film, cloth, and the like). In this method, since the recording head is not brought into direct contact with the record-receiving material, less noise is generated and silent recording is achieved. In addition, since features of reduced size and increased speed are readily achievable, the inkjet recording method has been rapidly popularized in recent years. Accordingly, great advancement of the method hereafter is expected as well.
In the inkjet recording method, an ink composition prepared by dissolving coloring agents, such as various dyes or pigments, in water or water and an organic solvent, and also containing a wetting agent formed by a water-soluble organic solvent is generally used.
In the inkjet recording method, in addition to inkjet exclusive paper or glossy paper for inkjet having an ink-receiving layer, general purpose plain paper with a low water absorption capacity, and the like may be used as a record-receiving material in some cases. Such a record-receiving material does not actively include an absorbing layer and it is difficult to impregnate the ink into the record-receiving material. Therefore, drying takes a long time.
For example, in the case of high-speed automatic duplex printing in which second-face printing is carried out by instantaneously reversing a piece of paper after the first side has been printed in an inkjet recording device, a problem of contamination of reversing rollers due to undried ink may occur.
Furthermore, when a concentration of the coloring agent in the ink composition is increased in order to increase image density, it is known that the stability of the ink deteriorates. Furthermore, due to drying in the vicinity of a nozzle, the coloring agent is deposited and thus the nozzle may be clogged with the coloring agent in some cases.
Therefore, an inkjet recording method in which drying is performed rapidly even in the case of the record-receiving material having no ink-receiving layer such as plain paper, the image density is high, and the image quality is high has been desired.
There are two kinds of coloring agent which may be used in an ink for inkjet, that is, a dye and a pigment. They each are widely used as a coloring material for inkjet. In general, it is known that a dye has low endurance to light or ozone gas, and that since a dye is soluble in water, the record-receiving material after printing has low resistance to water. On the other hand, it is known that a pigment is excellent in terms of various types of resiliance to light, ozone gas, water, or the like. However, since the pigment is insoluble in water, there is a defect in that, if the pigment is dried once and then agglomerated, the pigment cannot be dispersed again in water, which is likely to result in a problem.
Hence, in order to expand the field of application of printing methods using an ink, high color development and improvement of various types of resiliance, such as light resistance and water resistance, are demanded in ink compositions for use in inkjet recording and the colored body colored with the ink composition. In addition, in the ink composition for use in inkjet recording, it is strongly demanded that the ink composition has long-term stability as an ink or the ink composition can be dissolved or dispersed in water again when the ink composition is dried.
In particular, it is demanded that a pigment ink be stable for a long period of time. It is known that, in the pigment which is not present as molecules in the ink but is generally present as particles in a dispersed state, sedimentation phenomenon temporally occurs due to agglomeration of pigment particles. Accordingly, a concentration gradient occurs in the ink and thus there is a problem in that initial printing characteristics cannot be obtained, or, in the worst case, there is a problem in that agglomerated particles are clogged at a nozzle and thus cannot be discharged.
Therefore, there is a demand for development of an ink composition in which various types of resiliance are favorable, the density of an image to be obtained by printing is high, and storage stability is favorable when the pigment is used in the ink composition. However, as the case now stands, as yet there are just a few ink compositions with sufficient performance.
As an inkjet ink composition using a pigment, an ink of Patent Document 1 is given as an example. This is an ink composition obtained by preparing a dispersion using a polymer dispersion agent. In addition, Patent Document 2 discloses an ink composition using a self-dispersion pigment.
In recent years, a microcapsule pigment using a self-assembling pigment has been widely discussed and extensively discussed as a means for solving the above-described problems. Patent Document 3 discloses a method for producing the microcapsule pigment. However, all ink compositions have not been provided as a product sufficiently satisfying a need in the market yet.
Furthermore, various types of dispersion agents have been discussed in order to obtain a coloring agent dispersion for inkjet. Patent Documents 4 and 5 each disclose a method for producing a dispersion agent using a block polymer and a method for producing dispersion using the same.
Patent Document 6 discloses a method for producing a block polymer by using an organic tellurium compound, but does not disclose the use of the polymer as a dispersion agent or application of dispersion for inkjet.    Patent Document 1: Japanese Patent No. 3534395    Patent Document 2: Japanese Patent No. 4016483    Patent Document 3: Japanese Patent No. 4078679    Patent Document 4: PCT International Application, Publication No. 2010/013651    Patent Document 5: Japanese Patent No. 2675956    Patent Document 6: Japanese Patent No. 3839829    Non-Patent Document 1: DIC Technical Review No. 10/2004